Known mold tools for extrusion blow molding usually comprise two mold halves which are of a mutually complementary configuration and which jointly define a mold cavity. In the extrusion blow molding procedure, a thermoplastic extrudate, generally in the form of a tube, is put into position between the opened halves of the tool. The tool closes around the preform, the latter is applied within the tool against the inside wall of the cavity formed by the tool so that the finished article is of an external configuration corresponding to the internal contour of the mold tool. Shaping of the preform within the cavity of the tool is effected either by expansion of the preform by means of gas pressure or by virtue of the preform being applied against the inside wall of the tool by means of a reduced pressure which is produced by way of passages in the mold wall.
As already mentioned in the opening part of this specification, it is known both to expand extrudates in tube form within a mold tool and also to transform extrudates in the form of bands or webs in the tool. Simple blow molding molds are of a two-part nature, wherein the mold halves are arranged displaceably relative to each other on or in a closing frame structure. Within the closing frame structure the parts of the tool perform an opening and closing movement. Often the closing frame structure itself is also displaceable with respect to one or more stationarily arranged extrusion heads.
Hollow bodies such as bottles, canisters, tanks or the like are usually produced with the extrusion blow molding process. It will be appreciated that it is not possible to produce components involving severely undercut configurations with the blow molding process, at least not without the assistance of sliders in the tool. In addition parts in respect of which precise dimensional accuracy of the wall thickness is an important consideration cannot be produced in the blow molding process as the manner of manufacture means that only the external contour of the hollow body can be exactly reproduced. For that reason screwthreads or other component parts on containers in respect of which dimensional accuracy is an important consideration are often fitted into the mold tool in the form of an injection-molded insert portion, before the preform is introduced into the mold tool. A similar procedure is involved in applying labels to bottles (in-mold labeling).
In regard to many technical components it is desirable for insert portions to be placed within the hollow body. Particularly in the production of fuel tanks, valves, pumps, floats, surge containers and the like such insert portions must be fitted thereinto. They can be fitted into the tank during manufacture or fitted into the tank subsequently through openings.
For many different reasons it is particularly advantageous for insert portions to be already introduced into the hollow body during production thereof, in which case precise placement and fixing of the part in question in the tank to be produced often causes difficulties. It has long been known for insert portions to be also blow molded in position in the production of hollow bodies. That is usual for example in the production of battery casings of plastic material or other electronic units. In that case the electrodes or conductor tracks are placed beneath the extrusion head by means of a gripper in such a way that they are enclosed by the tubular extrudate. Upon subsequent closure of the mold and expansion of the preform, the plastic material of the preform in part flows through the element in question so that it is anchored firmly within the hollow body to be produced.
That is not so simple when a plurality of insert portions are to be placed in the hollow body in a predetermined spatial arrangement relative to each other. Then, fixing those insert portions to the inside wall of the hollow body and also exact positioning usually causes difficulties.
In the production of fuel tanks it would be desirable for example for valves, valve mounting means and fuel conduits connecting same to be fixed in the form of completely pre-assembled conduit manifolds to the inside wall of the tank in production thereof.
Therefore the object of the invention is to provide a novel tool which in the production of extrusion blow molded hollow bodies permits exact placement of a plurality of insert portions even when the hollow body is of a spatially complex configuration.